The present invention relates to a method of automatically determining the tool path in an operation for plane machining any zone or region of a workpiece, which zone is either a pocket (understood closed), or a so-called open pocket, or else a surfacing. This method applies both to the case where each of these three zones is considered alone, i.e. free of an islet or recess and to the case where each of these three zones contains at least one islet and/or at least one recess.
The following definitions are recalled:
a pocket is a zone of material to be machined whose outer profile is closed and which is surrounded by material not to be machined; PA1 an open pocket is a zone of material to be machined defined outwardly by a succession of walls and external contour edges of the workpiece, each wall defining a region of material not to be machined; PA1 a surfacing is a zone of material to be machined defined outwardly by the contour of the workpiece; PA1 an islet is a zone of material not to be machined whose outer profile is closed and which is located either inside a pocket or inside an open pocket, or inside a surfacing, thus forming an obstacle to be avoided during machining; PA1 a recess is an empty zone whose outer profile is closed and which is formed either in a pocket, or in an open pocket, or in a surfacing. PA1 minimizing the path of the axis of the tool; PA1 minimizing the number of downward and upward movements of the tool in the zone to be machined, and so the number of boreholes in said zone; PA1 to take into account the method of working of the tool (by swallowing, or in opposition); PA1 avoiding passing too many times over a location already machined; PA1 avoiding the incoming and outgoing traces of the tool. PA1 starting from the cross-ruling, in determining by their respective line and column indices, on the one hand, points, called limit points which are the apices of the cross-ruling the closest to the pocket profile, obtained by searching, in each line and each column of the cross-ruling, for the intersections with the profile and, on the other hand, the points situated respectively inside and outside the profile which are the apices of the cross-ruling left unoccupied by the limit points; PA1 tranferring to an intermediate table proper to the pocket profile and having the same dimensions and the same line and column pitch as the cross-ruling, in the same indexed line and column positions as those of the cross-ruling, the respectively limit, inner and outer points of the profile, representing them using respective identification symbols; PA1 in taking into account any first point of said zone, called starting point, and in assigning thereto a level represented by the integer 1; PA1 in taking into account a second point adjacent the starting point and situated on the same line or same column as the latter and assigning thereto a level represented by the integer 2; PA1 in then passing from a coded current point to the next point by searching among its neighbors to see if there exists a non coded point, this search taking place from the point which was coded previously to the current point and turning about the current point in the same predetermined search direction; if the non coded point exists, in assigning thereto a level represented by the integer n+1 if the level represented by the positive integer n is assigned to the current point; if the non coded point does not exist, in "back-tracking" until a coded point is found which has at least one non coded neighbor, this point becoming the current point the end of coding taking place when the "back-tracking" is effected as far as the starting point and when the latter has no longer a non coded neighbor; PA1 in determining first coded point called machining beginning point; PA1 to pass successively from a current point to the next point, said current point being at the outset the start of machining point, in searching among its neighbors for the "non machined" point of highest level and in determining whether this level is less or greater than that of the current point; if it is less, in considering the current point as "machined point" over which the tool does not pass again; if it is greater, in considering the current point as "waiting point" over which the tool may pass again. PA1 for each of the profiles considered and starting from the same cross-ruling, in determining by their respective line and column indices, on the one hand, points called limit points which are the apices of the cross-ruling the closest to the profile considered, obtained by searching in each line and each column of the cross-ruling for the intersections with the profile and, on the other hand, the points situated respectively inside and outside the profile which are the apices of the cross-ruling left unoccupied by the limit points; PA1 in transferring to an intermediate table proper to each of the profiles considered and having the same dimensions and the same line and column pitch as the cross-ruling, at the same indexed line and column positions as those of the cross-ruling, the respectively limit, inner and outer points of the profile considered, representing them by respective identification symbols; PA1 in so far as the pocket profile is concerned, in determining for each non machinable point of the second zone of the result table, the machinable points of the first zone whose distance to said non machinable point is less than the radius of the tool, and in transforming these machinable points into non machinable points to which the same second character is assigned; PA1 in so far as the islet profile is concerned, in determining for each non machinable point of the third zone of the result table, the machinable points of the first zone whose distance to said non machinable point is less than the radius of the tool, and in transforming these machinable points into non machinable points to which the same third character is assigned; PA1 in so far as the recess profile is concerned, in determining for each machinable point of the first zone of the result table, the void points of the fourth zone whose distance to said machinable point is less than the radius of the tool, and in transforming these void points into machinable points to which the same first character is assigned.
Furthermore, in a way known per se, the different profiles considered, respectively pocket, open pocket, surfacing, islet and recess are programmed separately and each consists, in the machining plane, of a section of straight line and /or arc of a circle segments.
Knowing the contour of the zone to be machined, defined in the machining plane, the problem which arises then is to sweep the zone to be machined completely with a cutter, without encroaching on the material limit defined as being the limit with a zone of material not to be machined (edge of pocket or islet) and respecting the following machining requirements as well as possible:
At the present time, one of the known plane machining techniques which seems to answer these machining requirements best uses an algorithm for obtaining movement of the tool by successive parallel shifts of the profile considered. However, this technique is very complicated to use, particularly when all the possible profile forms are to be taken into account. Moreover, its use has been limited up to now to the case of a pocket with a single islet or a single recess.
The object of the present invention is to provide a method for automatically determining the tool path during plane machining, which satisfies the above machining requirements, which may be used not only in the case of a pocket alone, an open pocket alone, or a surfacing alone, i.e. without islet or recess, but also in that of a pocket, an open pocket or surfacing with at least one islet and/or at least one recess, and which is rapid and relatively simple to put into practice.